COPEPODS GRAZING ON NODULARIA SP. AND SYANOBACTERIAL IMPACT ON GRAZING HIGH QUALITY FOOD

Cyanobacteria are considered inadequate food for some zooplankton. Characteristics like toxicity and morphology make cyanobacteria non-preferred food. We aimed at answering the questions: Are there species-specific differences between copepods grazing on cyanobacteria and at which rates do copepods graze on different filamentous strains? We performed grazing experiments with two abundant copepod species from the northern Baltic Sea, Eurytemora affinis and Acartia bifilosa. In the first experimental series, we fed toxic and non-toxic Nodularia sp. to the copepods. Eurytemora used the non-toxic strain as food and the toxic one to some extent. Acartia did not use either strain as food.
In the second experimental series, we hypothesized that increasing concentrations of toxic Nodularia decreases the uptake of high quality food in Acartia. We provided Acartia with a green alga, and added toxic Nodularia culture at different concentrations. The results suggest that feeding behaviour of copepods plays an important role in the interaction between cyanobacteria and copepods. The predominant suspension feeding Eurytemora was not able to avoid feeding cyanobacteria, and displayed negative effects due to toxin ingestion (mortality, deformed egg sacs, low egg production). Acartia, in contrast, as a relatively more selective species, was able to avoid ingesting cyanobacterial filaments and, hence, toxins.